There are several architectures for transmitting information from one electronic device to another. A commonly used architecture is shown in FIG. 1. In this architecture the devices share a common communication structure, often called a data bus or communication bus. Each device connected to the bus can transmit information on the bus, or receive any information transmitted on the bus. In addition the information transmitted on the bus can pass undistorted through each of the devices. The section of the communication bus connecting one device to another may be termed communication bus line or link. The physical medium through which the signal is transported can be an electrical wire or optical fiber. The signal transmitted from one device to another device on the communication bus can be a change in the voltage, an optical pulse, an electrical pulse with an underlying RF (radio frequency) modulation or similar implementations. Examples of such buses are Mil-Std-1553, CAN, FlexRay, RS485, RS42, and others. Since the transmitted signal passes through multiple devices, it is clear that the connection to each device should not cause any changes in the signal. When all devices have at most two bus links connecting the device to another device the bus is called one dimensional bus. If at least one device has three or more bus links to other devices the bus is called a two dimensional bus.
A commonly used communication bus is a two wire, differential signaling communication bus. In this bus there are two parallel communication buses connecting each device. The signal in this bus is the difference between the signal in one bus to the signal in the parallel bus. As an example, if each bus is an electric wire connecting the devices and if the signal is a voltage change in the wire, than in a differential bus, the signal is the voltage difference between the voltages on the two wires. Differential buses are used to overcome certain adverse physical conditions. For example if the bus suffers significant electrical interference, the voltage on one wire can be unpredictable and the bus would not function. However the two wire bus would see the same voltage interference on both wires and the resulting difference would not be impacted by the electrical interference. Hence a two wire differential bus provides better noise immunity. To prevent signal reflections at bus boundaries or at device to bus connection, the bus is designed with a characteristic impedance and the bus termination or connection points have a termination impedance which matches the bus impedance.
State of art differential buses with termination cannot detect a transmitted signal if there is a fault such as a cut or open circuit in one of the wires of the bus. In the case of a fault, the voltage on one line will follow the voltage on the second line due to the termination resistors (resistance) and there would not be the required voltage difference between the lines to indicate that a transmission has occurred. It is desirable to have a transceiver structure which can continue functioning even if there is a fault in the differential communication bus. Examples of a fault are a mechanical cut or other form of disconnect in one of the data bus wires. During the occurrence of such a fault the transmitted data on the data bus would be received with a large number of errors which can reduce the utilization of the data bus to less than 10% of its original capacity. Also, during the occurrence of such a fault the transmitted data on one side of the fault would not pass the fault and reach the units on the other side of the fault. In addition, in the case for self-erupting protocols such as CAN Bus, if one of the two wires is still intact, units transmitting at the same time on both sides of the bus fault would interfere with each other's transmissions. Hence, it is desirable to provide a data bus architecture which can reduce the number of transmission errors in the event of a fault in the differential data bus.